An Enterprise is modelled and studied based on the concepts of the methodology of complex activity. The proposed representation embraces the following key aspects of an Enterprise: Humans and their active choices as key elements of an Enterprise – Human Capital; Nontrivial structure of the subject matter of the control, which is defined by the goal/logical structure; Implementation of CA during all phases of its lifecycle; Technology of CA – the system of conditions, criteria, forms, methods, and means to successfully achieve a stated goal. Technology is incorporated in the Knowledge of the Enterprise. The Enterprise control problem is posed and solved as an aggregate of mathematical optimization problems. As a result, a harmonized set of mathematical models and methods is proposed that not only models the essential features of the Enterprise as a complex system of systems but also allows solving Enterprise control problems as formal mathematical optimization problems.